Service using the Internet of Things (IoT) has become widespread and been expanding these days, in which sensor devices having communication functions are remotely monitored and controlled, and a server collects and utilizes data measured by the sensor devices.
A typical example of the IoT service is a smart grid. The smart grid is a system in which a smart meter placed at each location measures the amount of electricity used at the location, and a server centrally manages power consumption by collecting the amounts of electricity used transmitted from the smart meters.
Meanwhile, the maintenance of the sensor devices involves updating firmware (or software) to cause the sensor devices to operate. In this case, the server transmits the firmware to the sensor devices, and the sensor devices that have received the firmware individually update their own firmware. Prior art documents include International Publication Pamphlet No. WO 2011/121671 and Japanese Laid-open Patent Publication No. 2008-306314.